OK! Exclusive: Katie Holmes Goes for Laughs

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Looks like Katie Holmes, who recently exercised her muscles in the New York City Marathon, has chosen to exercise her comedic acting chops with a cameo appearance in the upcoming film Tropic Thunder.

OK! can exclusively reveal that Mrs. Tom Cruise will join the film's star (and producer and director) Ben Stiller and co-stars Robert Downey, Jr., Jack Black and Nick Nolte in the (hopefully) funny flick about actors appearing in a low-budget war movie who are drafted into becoming real-life soldiers.

Shirtless stud Matthew McConaughey is also slated to make an appearance in a role initially written for Stiller's frequent co-star Owen Wilson, who pulled out of the film in August as he continues to recover from his suicide attempt.

As reported last week by OK!, Katie is still hoping to star in The Other Side, a fantasy/comedy set to start shooting in January in Nova Scotia, though the ongoing Writers' Guild Strike has placed that schedule in jeopardy.